Fix two more -Os strcoll / wcscoll build failures.

Continuing fixes for -Os build issues shown with build-many-glibcs.py,
this patch adds uses of DIAG_* to disable -Wmaybe-uninitialized in two
more places where code inlined from strcoll / wcscoll is wrongly
diagnosed as possibly using uninitialized structure fields.  (All
these warnings in different places for these functions are I think
essentially the same bug.)

Tested with build-many-glibcs.py for alpha-linux-gnu and
mips-linux-gnu that this fixes the -Os build failures for those
configurations with GCC 7.

	* locale/weightwc.h (findidx): Ignore -Wmaybe-uninitialized for
	-Os in two more places.